Vertebrate nonmuscle myosin IIs have been shown to play important roles in a variety of cellular processes such as cell motility, cytokinesis, and both cell-matrix and cell-cell adhesion. Previous work has shown cell organization and cell adhesion defects in mice ablated for NMHC II-A. These defects may be explained by loss of E-cadherin and beta-catenin localization from cell adhesion sites in A-/A- ES cells grown in culture and in the intact embryos. We are extending these studies to well-characterized epithelial cells in culture such as MDCK cells. We have localized nonmuscle myosins in these cells and are studying the relationship between myosin light chain phosphorylation, cell migration, and cell adhesion. In addition, we are characterizing the cardiac localization of NMHC II-B and II-C by confocal microscopy, especially with regard to components of the myocyte Z-lines and intercalated disks. In order to make transgenic mice that mimic the human syndrome known as May?Hegglin in which there are point mutations in MNHC II-A, we are isolating a genomic clone which contains the first coding exon of the NMHC II-A locus. This clone will also be used to generate mice with a fluorescent tag on the endogenous NMHC II-A as well as mice in which NMHC II-B replaces II-A and is under control of the II-A promoter.